Method of and device for controlled quenching light metal castings in a liquid bath

ABSTRACT

A method of controlled quenching of light metal castings in a liquid bath has castings in the liquid bath subjected, from below, at least temporarily, by a rising flow of gas bubbles. The gas bubbles are generated in situ in a uniformly distributed way at the base of the liquid bath.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims priority to German Patent Application 100 19 306.4 filed Apr. 19, 2000, which application is herein expressly incorporated by reference.

FIELD AND BACKGROUND OF THE INVENTION

[0002] The present invention relates to a method and device for controlled quenching light metal castings in a liquid bath. Quenching castings in a liquid forms a well-known part of heat treatment of both ferrous and non-ferrous metals. It is known to immerse castings in a water bath or an oil bath. Alternatively, the castings may be placed under a water shower. It is also common practice to cool castings in an air flow. Independent of the different rates of heat transition of liquid or gaseous cooling mediums, the status of free convection or forced flows, and as a function of the thermal capacity of the cooling medium and the thermal conductivity of the metal, it is possible to achieve different cooling speeds to form certain types of structures in the casting in different layer thicknesses.

[0003] JP 62-202019 A discloses a device which comprises a liquid-containing vessel. Pipe lines are introduced over the edge of the vessel. The pipe lines provide loop-shaped horizontally positioned lines to blow out gas. The parts to be hardened are lowered into the liquid-containing vessel by a carrying device. This occurs when gas is already emerging from the lines to blow out gas.

[0004] SU 1574648 A1 discloses a device which comprises a liquid-containing basin. The basin includes a side wall where a gas pressure line ends in the basin interior. The pressure line is followed by an injector to form a gas-bubble-enriched cooling stream. The parts to be hardened are lowered into the liquid by a gripping device.

SUMMARY OF THE INVENTION

[0005] It is an object of the present invention to improve the method and device so that it is easier to set the quenching process. In the method, the castings in the bath of liquid are subjected, from below, at least temporarily, to a rising flow of gas bubbles. The gas bubbles are generated in situ at the base of the liquid bath. The device comprises a tank filled with a liquid. The tank has at least one inlet and one outlet for the liquid. A gas bubble generating device is provided at the base of the tank. The gas bubble generating device has at least one air supply chamber at the base of the tank. The air supply chamber includes a cover with a plurality of gas exit apertures. Optionally, the gas bubbles are produced uniformly distributed in situ at the base of the liquid bath. Preferably, the castings are arranged at a distance above a zone of generating the gas bubbles. The liquid bath can be a water bath and the flow of gas bubbles can consist of air bubbles.

[0006] Immersing the castings into the liquid bath after the casting has been previously heated to a certain starting temperature, leads to prior art cooling curves. In accordance with the invention, it is possible by adding a gas bubble flow to clearly reduce or increase the cooling speed. In particular, by setting and regulating the flow of gas bubbles, it is possible to ensure that certain transformation temperatures for the structure are not prematurely undershot. The flow of gas bubbles does not have to be produced during the entire quenching process. On the contrary, the flow of gas bubbles can be switched off before the castings are finally removed from the liquid bath.

[0007] The inventive gas bubble generating device, at the base of the tank, may include at least one air supply chamber. The air supply chamber is closed by a cover having a plurality of gas exit apertures. The cover may include a porous plate. Here, if an over pressure in the air supply chamber exists, the porous plate enables a flow of gas bubbles to stream upwards in a uniformly distributed way. The porous plate, for example, may be an open metal foam, a porous ceramic material, or sintered metal. Further, a wire mesh element may be used as a cover for the air supply chamber. At the same time, it is advantageous to prevent any liquid from flowing into the air supply chamber. Since this cannot be completely prevented, it is recommended to provide an outlet for any liquid in the air supply chamber. The air supply chamber could include pressure control elements to control or set the flow of gas bubbles. The unitary air supply chamber may also be replaced by individual channels or lines with individual nozzle heads at the base of the tank. The nozzle heads may include a plurality of gas exit apertures.

[0008] Above the cover of the air supply chamber, a carrying base can be provided in the tank to deposit the castings. The carrying base includes relatively large through-apertures to enable the passage of the flow of gas bubbles.

[0009] A liquid supplied through an inlet can be cycled around the tank and be re-cooled in the process. Alternatively, it is possible to simply discharge overflow quantities of liquid or to use the liquid for other processes.

[0010] From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] An embodiment of the inventive device will be described below with reference to the drawings wherein:

[0012]FIG. 1 is a vertical section through a tank filled with liquid.

[0013]FIG. 2 is a plan view of a tank according to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014]FIG. 1 shows a tank 11 in the form of a cuboid which includes an upper opening 12 and a base 15. A cover 13 is positioned at a desired distance above the base 15. The cover 13 encloses an air supply chamber 14. The cover 13 is formed by a porous plate which includes a plurality of gas exit apertures. The cover 13 rests on a box profile 21 which is circumferentially placed about the base 15.

[0015] A carrying base 22 is positioned at a desired distance above the cover 13. The carrying base 22 receives the deposited castings.

[0016] The tank 11 is filled with a quenching liquid 16 above the cover 13. Gas bubbles 17 rise into the quenching liquid 16 from the air supply chamber 14 through the porous cover 13. The tank 11 includes a closable water outlet 19 near the upper opening 12 of the tank 11. A further water inlet 24 is provided to ensure a constant water level during the quenching process. A further water outlet 25 is provided above the carrying base 22.

[0017] The air supply chamber 14 is provided with a connector 20 for compressed air. A hose 26 is connected to connector 20 and pressure control element 28. The pressure control element 28 sets a continuous flow of bas bubbles into the tank 11. A water outlet 23 is arranged at the bottom of the air supply chamber 14.

[0018]FIG. 2 is a plan view of FIG. 1. FIG. 2 shows the tank 11 with the inserted carrying base 22, water inlets 18, 24 and water outlets 19, 25 for the quenching liquid, and the compressed air connector 20. Furthermore, it is possible to see the circumferential box profile 21.

[0019] While the above detailed description describes the preferred embodiment of the present invention, the invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims. 

What is claimed is:
 1. A method of controlling quenching light metal castings in a liquid bath comprising: placing castings in the liquid bath; subjecting the casting from below at least temporarily by a rising flow of gas bubbles; and generating the gas bubble flow in situ at a base of the liquid bath.
 2. A method according to claim 1 , further comprising uniformly distributing the gas bubbles at the base of the liquid bath.
 3. A method according to claim 2 , further comprising positioning the castings at a desired distance above a generating zone of the gas bubbles.
 4. A method according to claim 1 , further comprising pumping the liquid bath around in a cycle and re-cooling the liquid bath.
 5. A method according to claim 1 , further comprising constantly feeding new liquid into the liquid bath at the base of the liquid bath and that excess quantities of liquid being constantly discharged from the liquid bath.
 6. A method according to claim 1 , further comprising setting the flow of gas bubbles prior to the castings being fully immersed in the liquid bath.
 7. A method according to claim 1 , further comprising terminating the flow of gas bubbles before the castings are removed from the liquid bath.
 8. A device for controlled quenching light metal castings in a liquid bath, comprising: a tank to be filled with quenching liquid; at least one inlet and one outlet coupled with said tank for ingress and egress of liquid; a gas bubble generating device in said tank, said gas bubble generating device including a cover with a plurality of gas exit apertures positioned a distance from a base of said tank and at least one air supply chamber between said cover and the base of the tank.
 9. A device according to claim 8 , wherein a carrying base for receiving castings is positioned above the cover.
 10. A device according to claim 8 , wherein the cover includes a porous plate formed of an open metal foam, a porous ceramic material or sintered metal.
 11. A device according to claim 8 , wherein the cover being a wire mesh element.
 12. A device according to claim 8 , wherein a connector leads to the air supply chamber, said connector provided with a pressure control element for setting or controlling the flow of gas bubbles. 